White powdery mildew on the rise

I’m getting lots of Facebook and email images from folks seeing white powdery mildew, especially on crapemyrtles.

It seems to be on a cycle … I see it one year, then not for two or three. The last time I remember getting as many inquiries was in May 2017. So, that suggests to me that consistent rain and increasing humidity are causing the problem to ramp up.

What is powdery mildew? If you’re suddenly seeing grayish-white powder on the tips of your crapemyrtles, it’s likely you have it. In extreme cases, entire twigs may be blighted by the fungus. While it will not kill crapemyrtles, the blighted foliage detracts from the appearance of this popular southern landscape plant.

Leaves infected early in the season become curled and distorted as they expand. Infected younger leaves have blister-like areas which quickly become covered with the mildew. On older leaves, large white patches of fungus appear, but there is little leaf distortion. Flowers which originate from infected buds often become blighted.

Powdery mildew is most common in dry weather with warm days and cool nights – definitely sounds like the spring we enjoyed. If an infection isn't excessive, affected twigs may simply be removed by pruning. But heavily infected plants will probably require fungicide treatment for full recovery.

Crapemyrtles that have the worst experience are those that are over-pruned, or “massacred” in the winter. Crapemyrtles are trees, and trees should mostly be left alone. No other trees get pruned to the same spot, year in and year out!

Homeowners who have had severe powdery mildew problems in the past should start fungicide applications immediately after the first sign of the disease. It may be necessary to continue fungicide sprays until leaves are mature, at which time they are less susceptible to the fungus. Fungicide can also be applied during the flowering period to prevent blossom blight. Incidentally, powdery mildew also affects roses (below), annuals, perennials, vegetables and others.

Fungicides to Wash It Off

  • Consan 20 (or just Consan)
  • Neem oil
  • Banner-based fungicides (Bonide Infuse, Fertilome Liquid Systemic, Ortho Banner-based)
  • Homemade baking soda spray (2 teaspoons of baking soda, 2 quarts of water, ½ teaspoon of dish soap or Murphy’s Oil Soap)

Fungicides to Prevent It

• Any copper-based fungicide

  • Kocide
  • Liqui-Cop
  • Bonide Copper Fungicide

• Systemic fungicides with Mancozeb

• Banner-based fungicides (anything with PPZ, such as Bonice Infuse above)

By the way, you may have wondered why I used the spelling “crapemyrtle” here. Even in my most recent books I’ve spelled it “crape myrtle.” Both spellings are accepted, but to be “technically correct” in this tip, I decided to stay true to the tree’s genealogy. The common name is crapemyrtle, not crape myrtle. Why? Because it is in the genus Lagerstroemia and in the Lythraceae plant family - not in the genus Myrtus, which is in the Myrtaceae family.

There are also many people, especially in the South, who spell it “crepe myrtle.” So, which is correct? Short answer: It can actually be spelled both ways. Crape/crepe refers to the crinkled edges of the flower. Crape is the older spelling, but I am not sure that makes it correct. However, the American Crape Myrtle Society spells it with the 'a,' so I would use that. But I think I might spell it with an 'e' if writing, perhaps, for a Southern Living-type magazine.


IMAGES: Crape myrtle - Growers Outlet; Roses - Randy Lemmon